(Supported in part by NIH GMS 40198 to C.L. Rieder). As outlined in one of our TRD projects, we have developed methods that allow us to generate centrosome free cells by using GFP-tagged gamma tubulin to light up the centrosome for subsequent destruction by laser microsurgery. Using this approach we are studying the role of the centrosome during the cell cycle in CV1 (greeen monkey kidney fibroblast) cells. The first question we are asking is how the existing microtubule array is modified when the centrosome is destroyed and if, after destroying the centrosome and disassembling the existing microtubules by cooling, it reforms when the cell is re-warmed. We are also asking if cells lacking centrosomes are capable of proceeding normally through the cell cycle. The only way to conduct these studies is to use the BMIRR laser facility to create centrosome-free cells.